Gallic acid as potential sequestering agent for methylmercury(II) and dimethyltin(IV) removal from aqueous solutions

Organometal cations are dangerous pollutants of natural waters, causing severe environmental and biological problems. In contrast, gallic acid (GA) is a naturally occurring polyphenol found in citrus fruit peels, honey, grapes, hops, oak bark, and tea leaves, displaying several beneficial properties. Performing a contaminant speciation study in conditions simulating the ones characteristic of real environmental matrices, is essential for gaining information on the pollutant mobility, transport, toxicity, environmental impact and fate. In this light, an investigation on the GA stability and acid-base properties, as well as, for the first time, on the ligand interactions with two organometal cations, namely methylmercury(II) (CH3Hg+) and dimethyltin(IV) ((CH3)2Sn2+), was carried out by means of potentiometry, UV–VIS spectrophotometry, 1H NMR spectroscopy and spectrofluorimetry. The thermodynamic data showed for gallic acid higher complexation and sequestering abilities towards dimethyltin(IV) with respect to methylmercury(II), demonstrating the ligand promising and selective performances as potential decontaminating agent for the (CH3)2Sn2+ remediation from polluted sites. This study could also contribute to the development of environmental strategies aimed at the production of new gallic-acid based sustainable materials dealing with the organometal contamination issue, as well as for potential applications in various industrial fields.